Two different zinc(II)-aqua complexes held up by a metal-oxide based support: synthesis, crystal structure and catalytic activity of [HMTAH]₂[{Zn(H₂O)₅}{Zn(H₂O)₄}{Mo₇O₂₄}]·2H₂O (HMTAH = protonated hexamethylenetetramine)

Abstract

An inorganic-organic hybrid material, [HMTAH]₂[{Zn(H₂O)₅}{Zn(H₂O)₄}{Mo₇O₂₄}]·2H₂O (1) (where HMTAH = protonated hxamethylenetetramine) has been synthesized and structurally characterized. The compound 1 crystallizes in a monoclinic space group C2/c. The crystal data of 1: α = 43·12(3), b = 12·399(10), c = 16·285(13), β = 111·131(11), Z = 8. Its crystal structure shows that two different Zn(II)-aqua complexes, [Zn(H₂O)₅]²⁺ and [Zn(H₂O)₄]²⁺ are covalently coordinated to a heptamolybdate anion [Mo₇O₂₄]^6- resulting in an anionic species of polyoxometalate supported zinc-aqua complexes, [{Zn(H₂O)₅}{Zn(H₂O)₄}{Mo₇O₂₄}]^2-, that is stabilized with two protonated hexamethylenetetramine cations in the title compound 1. In the crystal structure, both lattice water molecules are found to interact with the heptamolybdate cluster anion and the protonated hexamethylenetetramine cation resulting in an intricate three-dimensional hydrogen bonding network. Interestingly, compound 1 exhibits catalytic activity towards oxidation of some primary alcohols.